Voltage regulator and power receiving apparatus

Abstract

The voltage regulator includes a resistor circuit that switches between a first state and a second state according to the comparison result signal. In the first state, a resistance between a second end of a first controlling transistor and a fixed potential is set at a first resistance, and a second end of a second controlling transistor and the fixed potential are disconnected from each other. In the second state, the second end of the first controlling transistor and the fixed potential are disconnected from each other, and a resistance between the second end of the second controlling transistor and the fixed potential is set at a second resistance.

What is claimed is: 
     
       1. A voltage regulator comprising:
 an output transistor that is connected to a power supply terminal at a first end of a current path thereof and to an output terminal, at which the output voltage is output, at a second end of the current path thereof, a first voltage being supplied to the power supply terminal; 
 a first detecting transistor that is connected to the power supply terminal at a first end of a current path thereof and to a gate of the output transistor at a gate thereof; 
 a first controlling transistor that is connected to a second end of the current path of the first detecting transistor at a first end of a current path thereof; 
 a first amplifying circuit that controls a gate voltage of the first controlling transistor so as to make a voltage at the second end of the current path of the output transistor and a voltage at the second end of the current path of the first detecting transistor equal to each other; 
 a second detecting transistor that is connected to the power supply terminal at a first end of a current path thereof and to the gate of the output transistor at a gate thereof; 
 a second controlling transistor that is connected to a second end of the current path of the second detecting transistor at a first end of a current path thereof; 
 a second amplifying circuit that controls a gate voltage of the second controlling transistor so as to make the voltage at the second end of the current path of the output transistor and a voltage at the second end of the current path of the second detecting transistor equal to each other; 
 a third amplifying circuit that controls a gate voltage of the output transistor so as to make a first reference voltage and the output voltage equal to each other; 
 a comparator that compares the first voltage and the output voltage, and outputs a comparison result signal that is based on a result of the comparison; and 
 a resistor circuit that includes a first resistor having a first resistance between the second end of the current path of the first controlling transistor and a fixed potential and a second resistor having a second resistance between the second end of the current path of the second controlling transistor and the fixed potential, wherein 
 a detected voltage that is based on a voltage at the second end of the current path of the first controlling transistor is output at an output node in a first case where the potential difference between the first voltage and the output voltage is equal to or greater than a reference value, and 
 the detected voltage that is based on a voltage at the second end of the current path of the second controlling transistor is output at the output node in a second case where the potential difference is smaller than the reference value. 
 
     
     
       2. The voltage regulator according to  claim 1 ,
 wherein the first resistance and the second resistance are different from each other. 
 
     
     
       3. The voltage regulator according to  claim 1 ,
 wherein the first resistance is determined so as to set the voltage at the second end of the current path of the first controlling transistor at a preset target value, in a case where the potential difference is equal to or greater than the reference value, and 
 the second resistance is determined so as to set the voltage at the second end of the current path of the second controlling transistor at the target value, in a case where the potential difference is smaller than the reference value. 
 
     
     
       4. The voltage regulator according to  claim 1 ,
 wherein a size of the first detecting transistor is set to be smaller than a size of the output transistor, and 
 a size of the second detecting transistor is set to be smaller than the size of the output transistor. 
 
     
     
       5. The voltage regulator according to  claim 1 ,
 wherein, in the resistor circuit, 
 the first resistor is a first variable resistor, and 
 the second resistor is a second variable resistor, and 
 wherein the resistor circuit comprises: 
 a switch circuit that switches between the first case and the second case, and 
 in the first case, the second end of the current path of the first controlling transistor and the output node are connected to each other, and the second end of the current path of the second controlling transistor and the output node are disconnected from each other, and 
 in the second case, the second end of the current path of the first controlling transistor and the output node are disconnected from each other, and the second end of the current path of the second controlling transistor and the output node are connected to each other. 
 
     
     
       6. The voltage regulator according to  claim 1 ,
 wherein the resistor circuit is a variable resistor in which the first resistor and the second resistor are in common, and 
 the variable resistor is arranged between the output node and the fixed potential, and 
 the resistor circuit comprises: 
 a switch circuit arranged between the output node, the second end of the current path of the first controlling transistor and the second end of the current path of the second controlling transistor; and 
 a controlling circuit, and 
 wherein the controlling circuit sets the resistance of the variable resistor at the first resistance, in the first case, and 
 the controlling circuit sets the resistance of the variable resistor at the second resistance, in the second case, and 
 wherein the switch circuit connects the output node and the second end of the current path of the first controlling transistor to each other, and disconnects the output node and the second end of the current path of the second controlling transistor from each other in the first case, and 
 the switch circuit disconnects the output node and the second end of the current path of the first controlling transistor from each other, and connects the output node and the second end of the current path of the second controlling transistor to each other in the second case. 
 
     
     
       7. The voltage regulator according to  claim 1 , further comprises:
 an analog-to-digital converting circuit that analog-to-digital converts the detected voltage. 
 
     
     
       8. The voltage regulator according to  claim 1 , wherein
 the comparator that compares the first voltage and the output voltage plus the reference value. 
 
     
     
       9. A voltage regulator comprising:
 an output transistor that is connected to a power supply terminal at a first end of a current path thereof and to an output terminal, at which the output voltage is output, at a second end of the current path thereof, a first voltage being supplied to the power supply terminal; 
 a first detecting transistor that is connected to the power supply terminal at a first end of a current path thereof and to a gate of the output transistor at a gate thereof; 
 a first controlling transistor that is connected to a second end of the current path of the first detecting transistor at a first end of a current path thereof; 
 a first amplifying circuit that controls a gate voltage of the first controlling transistor so as to make a voltage at the second end of the current path of the output transistor and a voltage at the second end of the current path of the first detecting transistor equal to each other; 
 a third amplifying circuit that controls a gate voltage of the output transistor so as to make a first reference voltage and the output voltage equal to each other; 
 a comparator that compares the first voltage and the output voltage, and outputs a comparison result signal that is based on a result of the comparison; and 
 a variable resistor having a first resistance between the second end of the current path of the first controlling transistor and a fixed potential, 
 a controlling circuit that sets the resistance of the variable resistor at a first resistance, in a case where the potential difference is equal to or greater than a reference value, in response to the comparison result signal, and sets the resistance of the variable resistor at a second resistance, in a case where the potential difference is smaller than the reference value, in response to the comparison result signal, the second resistance being different from the first resistance. 
 
     
     
       10. The voltage regulator according to  claim 9 , further comprises:
 an analog-to-digital converting circuit that analog-to-digital converts the detected voltage. 
 
     
     
       11. The voltage regulator according to  claim 9 , wherein
 the comparator that compares the first voltage and the output voltage plus the reference value. 
 
     
     
       12. A power receiving apparatus that receives electric power transmitted from a power transmitting apparatus by wireless power supply, rectifies an obtained current and outputs the rectified current, comprising:
 a power receiving coil that is connected between a first power receiving terminal and a second power receiving terminal and is electromagnetically coupled to a power transmitting coil in the power transmitting apparatus; 
 a power receiving capacitor that is connected in series with the power receiving coil between the first power receiving terminal and the second power receiving terminal; 
 a rectifying device that rectifies a voltage between the first power receiving terminal and the second power receiving terminal and supplies a first voltage to a power supply terminal; 
 a voltage regulator that outputs an output voltage, which is generated from the first voltage at the power supply terminal, at an output terminal; and 
 a load circuit to which the output voltage is supplied, 
 wherein the voltage regulator includes: 
 an output transistor that is connected to a power supply terminal at a first end of a current path thereof and to an output terminal, at which the output voltage is output, at a second end of the current path thereof, the first voltage being supplied to the power supply terminal; 
 a first detecting transistor that is connected to the power supply terminal at a first end of a current path thereof and to a gate of the output transistor at a gate thereof; 
 a first controlling transistor that is connected to a second end of the current path of the first detecting transistor at a first end of a current path thereof; 
 a first amplifying circuit that controls a gate voltage of the first controlling transistor so as to make a voltage at the second end of the current path of the output transistor and a voltage at the second end of the current path of the first detecting transistor equal to each other; 
 a second detecting transistor that is connected to the power supply terminal at a first end of a current path thereof and to the gate of the output transistor at a gate thereof; 
 a second controlling transistor that is connected to a second end of the current path of the second detecting transistor at a first end of a current path thereof; 
 a second amplifying circuit that controls a gate voltage of the second controlling transistor so as to make the voltage at the second end of the current path of the output transistor and a voltage at the second end of the current path of the second detecting transistor equal to each other; 
 a third amplifying circuit that controls a gate voltage of the output transistor so as to make a first reference voltage and the output voltage equal to each other; 
 a comparator that compares the first voltage and the output voltage, and outputs a comparison result signal that is based on a result of the comparison; and 
 a resistor circuit that includes a first resistor having a first resistance between the second end of the current path of the first controlling transistor and a fixed potential and a second resistor having a second resistance between the second end of the current path of the second controlling transistor and the fixed potential, wherein 
 a detected voltage that is based on a voltage at the second end of the current path of the first controlling transistor is output at an output node in a first case where the potential difference between the first voltage and the output voltage is equal to or greater than the reference value, and 
 the detected voltage that is based on a voltage at the second end of the current path of the second controlling transistor is output at the output node in a second case where the potential difference is smaller than the reference value. 
 
     
     
       13. The power receiving apparatus according to  claim 12 ,
 wherein the first resistance and the second resistance are different from each other. 
 
     
     
       14. The power receiving apparatus according to  claim 12 ,
 wherein the first resistance is determined so as to set the voltage at the second end of the current path of the first controlling transistor at a preset target value, in a case where the potential difference is equal to or greater than the reference value, and 
 the second resistance is determined so as to set the voltage at the second end of the current path of the second controlling transistor at the target value, in a case where the potential difference is smaller than the reference value. 
 
     
     
       15. The power receiving apparatus according to  claim 12 ,
 wherein a size of the first detecting transistor is set to be smaller than a size of the output transistor, and 
 the size of a second detecting transistor is set to be smaller than the size of the output transistor. 
 
     
     
       16. The power receiving apparatus according to  claim 12 ,
 wherein, in the resistor circuit, 
 the first resistor is a first variable resistor, and 
 the second resistor is a second variable resistor, and 
 wherein the resistor circuit comprises: 
 a switch circuit that switches between the first case and the second case, and 
 in the first case, the second end of the current path of the first controlling transistor and the output node are connected to each other, and the second end of the current path of the second controlling transistor and the output node are disconnected from each other, and 
 
       in the second case, the second end of the current path of the first controlling transistor and the output node are disconnected from each other, and the second end of the current path of the second controlling transistor and the output node are connected to each other. 
     
     
       17. The power receiving apparatus according to  claim 12 ,
 wherein the resistor circuit is a variable resistor in which the first resistor and the second resistor are in common, and 
 the variable resistor is arranged between the output node and the fixed potential, and 
 the resistor circuit comprises: 
 a switch circuit arranged between the output node, the second end of the current path of the first controlling transistor and the second end of the current path of the second controlling transistor; and 
 a controlling circuit, and 
 wherein the controlling circuit sets the resistance of the variable resistor at the first resistance, in the first case, and 
 the controlling circuit sets the resistance of the variable resistor at the second resistance, in the second case, and 
 wherein the switch circuit connects the output node and the second end of the current path of the first controlling transistor to each other, and disconnects the output node and the second end of the current path of the second controlling transistor from each other, in the first case, and 
 the switch circuit disconnects the output node and the second end of the current path of the first controlling transistor from each other, and connects the output node and the second end of the current path of the second controlling transistor to each other, in the second case. 
 
     
     
       18. The power receiving apparatus according to  claim 12 , further comprises:
 an analog-to-digital converting circuit that analog-to-digital converts the detected voltage. 
 
     
     
       19. The power receiving apparatus according to  claim 12 , further comprises:
 a capacitor connected between the power supply terminal and the fixed potential. 
 
     
     
       20. The power receiving apparatus according to  claim 12 , wherein
 the comparator that compares the first voltage and the output voltage plus the reference value.